1. Field of The Invention
This invention relates to blending selected quantities of different types of fibers. More particularly, this invention relates to aspects of the blending system associated with weighing the different types of fibers.
2. Description of The Prior Art
To blend fibers, it has been well known to provide each different type of fiber in the blend to a different feeder. The feeders separate fibers and gradually accumulate them in a "weigh pan". When a predetermined weight of each type of fiber has been collected in each feeder, the feeders dump those fibers on a conveyor for transporting the fibers to a blender which mixes tne fibers into a more uniform blend. U.S. Pat. No. Re. 25,609 discloses such a blending system.
Typically, cut-off doors control whether fibers may reach the "weigh pan". Once the predetermined weight of fibers has accumulated in each feeder, the cut-off doors for that feeder are actuated to prevent further filling. Then, trap doors associated with the weigh pans for all the feeders open to dump the accumulated fibers on the conveyor. The cut-off doors and trap doors may be operated, for example, by solenoid valves. Examples of such feeders are disclosed in U.S. Pat. No. 3,421,659, 3,142,348, 3,132,709, 3,111,857 and 2,995,783. The feeders in these patents all must weigh fibers that have accumulated in the weigh pan. In these patents and U.S. Pat. No. 3,196,967, specifically directed to a weighing mechanism, the weigh pan is attracted to a magnet. As soon as a sufficient amount of fiber has accumulated in the weigh pan, it breaks away from the magnet, opening the trap doors.
Several features of such a magnetic system make it inconvenient. For example, the weight of fibers at which break-away occurs is controlled by adjusting the distance between a stop against which the weigh pan rests and the magnet. The adjusting process requires numerous fillings of the weigh pan to monitor the breakaway force. This proves to be quite time consuming. Also, the nature of this system is inherently less accurate than might be desired.
The systems in the above-cited patents are electro-mechanical and do not provide any automatic indication of the proper operation of the apparatus. Generally, mechanical means are employed to synchronize the various elements of the blending system. U.S. Pat. No. 3,225,848 discloses an electrically controlled system which helps to integrate the controlling function. U.S. Pat. No. 3,659,279 discloses an electrical system for monitoring for malfunctions.
To overcome the difficulties associated with employing a magnet to perform the weighing function, it has been known to employ electronic transducers to accomplish the weighing operation. Thus, U.S. Pat. No. 3,918,539 discloses wires to support the weigh pan whose resistance varies with the weight supported. Electronic weighing is also employed in equipment manufactured by Frontier Electronics and Hollingsworth Corp. both of South Carolina.
Systems for monitoring the quantity of fibers dumped by the respective feeders are also, in general, known. An example of such a system is described in U.S. Pat. No. 4,310,060.